Question: Expand. If necessary, combine like terms. $(3x+7)(3x-7)=$
Solution: Notice that this expression has the following special form: $(a+b)(a-b)$ This form expands to what we call "a difference of squares": $( a+ b)( a- b)= a^2- b^2$ Using the above pattern, we get: $\begin{aligned} ({3x}+ 7)({3x}- 7)&=({3x})^2- 7^2 \\\\ &=9x^2-49 \end{aligned}$